Color detection apparatus for multiple color printing



April 2, 1968 Original Filed Feb. 23, 1962 RELATIVE RESPONSE,

'J. c. FROMMER ETAL 3,376,426

COLOR DETECTION APPARATUS FOR MULTIPLE COLOR PRINTING 6 Sheets-Sheet 1-o 460 so'o edo 70'0 ado d b WAVELENGTHS, MILLIMICRONS 6 IN'VENTORSJOSEPH C. FROMMER, BY WARREN L. RHODES April 968 J. c. FROMMER ETAL3,376,426

COLOR DETECTION APPARATUS FOR MULTIPLE COLOR PRINTING Original FiledFeb. 25, 1962 6 heets-Sheet 2 LIGHT YELLOW MAGENTA C A YELLOW WW MEDIUMI l HEAVY Y YELLOW YELLOW FIG. 6

Ga Go I I A T I Gb Gb Yb Yb LJYC' LLL F IG. 8

INVENTORS JOSEPH C. FROMMER BY WARREN L. RHODES ATTYS.

April 2, 1968 J. c. FROMMER ETAL COLOR DETECTION APPARATUS FOR MULTIPLECOLOR PRINTING 6 Sheets-Sheet .5

Original Filed Feb. 23, 1962 -/PEAK REPRESENTATIVE SCALAR AVERAGE "FIG.9

PEAK

REPRESENTATIVE SCALAR AVERAGE FIG. 10

FIG. 31

32 (VIOLET) (RED) 39 VII m S S E 5W w 000 T MFR VCL. m N PE R Sm NWW Y BApril 1963 J. c. FROMMER ETAL 3,376,426

COLOR DETECTION APPARATUS FOR MULTIPLE COLOR PRINTING Original FiledFeb. 23, 1962 6 heets-Sheet 4 0 0 [L2 9 n g mv A 8 08 WW I c m8 -v- U Am 0) s I\ m k i N VI 60 no 0 g; -u

lnvnfors Joseph C. Frommer By Warren L. Rhodes.

A ril 2, 1968 J. c. FROMMER ETAL. 3,376,426

COLOR DETECTION APPARATUS FOR MULTIPLE COLOR PRINTING Original FiledFeb. 23, 1 962 I I 6 Sheets-Sheet 5 INVENTORS JOSEPH C. FROMMER BYWARREN L.RHODES W ATTYS ApriI 2, I968 J. c, FROMMER ETAL COLOR DETECTIONAPPARATUS FOR MULTIPLE COLOR PRINTING a Sheets-Sheet If Original FiledFeb. 23, 1962 INVENTORS JOSEPH C. FROMMER WARREN L. RHODES M 7414.

ATTYS.

United States Patent 3,376,426 COLOR DETECTION APPARATUS FOR MULTIPLECGLOR PRINTING Joseph C. Frommer, (Ziucinuati, Ohio, and Warren L.

Rhodes, Rochester, N.Y., assignors to Hurletron Incorporated, Danville,Ill., a corporation of Delaware Continuation of application Ser. No.453,537, Apr. 16, 1965, which is a continuation of application Ser. No.174,694, Feb. 23, 1962. This application Nov. 4, 1966, Ser. No. 592,227

Claims. (Cl. 250-226) This application is a continuation of ourapplication Ser. No. 453,357, filed Apr. 16, 1965, which was acontinuation of our application Ser. No. 177,694, filed Feb. 23, 1962.

This invention relates to automatic inspection means for monitoring theappearance of a number of non-spectrum colored inks comprising an imageapplied to a web. More particularly, in an important aspect, thisinvention relates to means for continuously and rapidly monitoring thedensities of each of the non-spectrum colored inks comprising amulticolored pattern which is printed on a rapidly moving web.

Photoelectric devices for inspecting a web for discolorations, flaws inthe material and other relatively coarse characteristics are well known;however, they have not heretofore been adapted successfully to monitorchanges in appearance of colored inks printed on the web in applicationssuch as 4-color magazine printing.

The reason for this is that the photoelectric transducer, such as thephototube, is not sensitive to color in the psychophysical manner thatthe human observer is. Instead, it is sensitive to elemtromagneticradiation in discreet ranges of wavelengths of the light spectrum. Aphotoelectric transducer comprising proper filters can be made torespond to light of a particular frequency which, if in the visibleband, would be observed by a human as one of the spectrum colors. It isin this limited sense that a photoelectric transducer can be describedas being sensitive to red, blue, or green light, or light of any of theother spectrum colors, which, in the case of this description, includescolors outside the visible spectrum, such as a particular range ofwavelength in the infra-red portion of the spectrum. A photoelectrictransducer, however, cannot be made selectively sensitive to anon-spectrum color such as magenta, cyan, yellow or black, the colorscommonly used in magazine printing. The reason is that magenta is thepsychophysical resultant of the mixture of red and blue lights. Thus aphotoelectric transducer sensitive to red light of 650 millirnicronswavelength cannot distinguish between a red light of that wavelength anda magenta light comprising a 650 millimicron red component and a 450millimicron blue component.

In certain applications, however, the density of magenta ink, which isan indication of its appearance to a hu man observer, can be monitoredby measuring the amount of incident green light which is absorbed by theink. One of these applications, to be described below in detail, is4-color magazine printing using magenta, cyan and yellow transmissiveinks and carbon black ink on a white web. In this case the density ofthe magenta ink is an inverse function of the amount of green lightwhich is refiected back from the white web through the transmissivemagenta ink.

Accordingly, it is the principal object of this invention to provide amethod and means for monitoring the appearance of a plurality ofnon-spectrum color inks applied to a web.

Another object of the invention is to provide a method and means foraccomplishing the principal object when 3,376,426 Patented Apr. 2, 1968one of the inks, such as black, has a high density in the infra-redrange of light wavelength.

Still another object of the invention is to provide a method and meansfor accomplishing the above objects when the inks are applied to arapidly moving web.

A further object of this invention is to provide nonspectrum colormonitoring apparatus including a combined subtractive and additivesuppression matrix responsive to spectrum colors.

An additional object of this invention is to provide color monitoringmeans having a magnetic memory synchronously operative with the repeatedprinting of a colored pattern on a web.

These and other objects and advantages of this invention will appearfrom the following description of a preferred embodiment of thisinvention adapted for use with a 4-color magazine printing press usingcyan, magenta and yellow transmissive inks and carbon black ink.

In the drawings:

FIG. 1 is a graph of the density characteristics of the yellow, magenta,cyan and black inks chosen for printing one magazine.

FIG. 2 is a graph of the photoelectric transducer responsecharacteristics of a particular combination of phototubes and opticalfilters for use with inks having characteristics similar to those shownin FIG. 1.

FIG. 3 is a diagrammatic plan view of a web printed with two differentcolors, magenta and yellow.

FIG. 4 is a graphic representation of the electrical signals obtainedfrom two of the phototubes in the scanner when scanning along the linesa, b, and c of FIG. 3 as a function of time.

FIG. 5 is a graphic representation of the output signals received fromthe suppression matrix as a result of applying the signals of FIG. 4 tothe suppression matrix input, as a function of time.

FIG. 6 is a diagrammatic plan view of a page printed with magenta andyellow inks, the yellow ink being printed in three different tones.

FIGS. 7 and 8 correspond to the FIGS. 4 and 5.

FIGS. 9 and 10 represent two time curves or oscillograms of two matrixoutput signals and three scalars commonly used to indicate theappearance of printed inks.

FIG. 11 is a diagrammatic sectional view through the scanner of thisinvention.

FIG. 12 is a circuit diagram of the amplifier, matrix and scalargenerator of this invention for one of the colors.

FIG. 13 is a perspective view showing an arrangement in which thescanner housing is driven laterally across the web and a magneticrecorder is synchronized to the scanner for recording scanner signals.

FIG. 14 is a circuit diagram of a modified form of the inventioncomprising an addition to FIG. 12 which may be used in connection withthe embodiment of FIG. 13.

FIG. 15 is a view of the face of cathode ray tube showing the displayprovided by the circuit of FIG. 14.

In order to obtain the desired quality of color printing from aletterpress, it is necessary to have the various printing cylindersproperly engraved and the application of ink to each cylinder carefullymetered. Metering is controlled by a ratchet acting over the entirewidth of the web and by keys, each acting only over a web width ofapproximately two inches. The ratchet and all keys have to be set toapply the right amount of ink. In the past, color patches of each colorhave been printed on certain designated portions of the pattern for thepurpose of photoelectric inspection of their color. These color patchesmust not detract from the appearance of the picture of the material tobe printed or they must be cut out and wasted before ultimate use of theprinted material. One such patch corresponding to each key is usuly notfeasible economically.

This present invention does not rely on specially printed color patches,but inspects the printing as it actually appears in the completed form.The photoelectric signals obtained from this inspection are submitted toan electrical analysis which yields specific information on the lack orsurplus of each colored ink.

This analysis comprises the following steps: A number of observationtracks along the width of the web are observed photoelectrically byconcentrating light thereon. Each track is called an inspection zone.The light reflected from the non-spectrum colored inks within aninspection zone is broken up into a number of spectrum components whichare the color complements of the non-spectrum inks. Each of the spectrumcomplements is fed to a separate phototube. The output signals of thesehototubes are processed so as to obtain signals which are indicative ofthe intensities of the several spectrum components incident on theindividual photototubes. Since these spectrum components are the colorcomplements of the non-spectrum colored inks being applied to the web,the measurement of the density of each nonspectrum ink is beingaccomplished by a measurement of the absorption of its color complement.These signals are fed into a suppression matrix which suppresses thoseportions of each signal which contain spurious information, such as thatportion of a signal which is representative of the overlapping ofcolors. From each of these resulting signals a scalar quantity isderived which is indic- 3 ative of the lack or excess of the respectivecolor ink in the inspected track. These scalars are displayed in a waywhich aids the pressman in making readjustments in the density of any ofthe colors. A number of preselected tracks can be inspectedsimultaneously by using one such for black at most points on the visibleportion of the spectrum.

FIG. 2 depicts the spectral response curves obtained withlamp-.mirror-filter-phototube combinations to ;be

more fully described in connection with FIG. 11. These combinations arereferred to as V (violet), G (green), R (red), and l (infra-red)according to the spectrum color to which they are maximally reactive.The abscissas again represent wavelength in millimicrons and theordinates indicate values linearly proportional to the signal output ofeach of the respective phototubcs and their associated optical andelectrical circuits in response to exposure of each phototube to lightof a given'wavelength. With the aid of the curves of FIGS. 1 and 2, theresponse of the various phototubes to paper printed with the variousnonspectrum inks can be determined as described hereinafter.

First, the area under each of the curves of FIG. 2 is calculated, asthis area is indicative of the photoelectric response of the respectivephototube to white paper. Next, each ordinate of a curve of FIG. 2 ismultiplied by the reciprocal of the antilogarithm of the respectiveordinate of one of the curves of FIG. 1. The resulting ordinates areused to determine the area under the curve obtained with theseordinates. This area will be proportional to,

White Yellow Magenta Cyan Black Violet response 1 .062 496 765 014 Greenresponse. 1 66 .12 .52 .021 Red response 1 .84 .895 .257 .048 Infra-Red1 .91 91 .91 09 system for each track, but, in a preferred embodiment ofthe invention, a single unit can inspect one track after another bymoving laterally across the width of the web, preferably, by the widthof one inspection track for each revolution of the printing cylinders.

FIG. 1 represents the spectral curves of the densities of samples ofyellow, magenta, cyan and black ink printed on white paper. Hereinafter,references to a web of white paper and to white level signals relate tothe fact that it is conventional for the printing web generally to be ofwhite paper and therefore readily enabling a white or base signal level.It is to be understood that webs of other color and material could alsobe easily employed, with appropriate adjustment of parameters of thisinvention.

The abscissas of curves in FIG. 1 represent wavelength in millirnicrons.The ordinates indicate units of density of ink applied to unprintedwhite paper. These curves show that the yellow ink has a maximum densityin the 400 to 500 millimicron range of wavelength, the magenta ink has amaximum density in the 500 to 580 millimicron range, the cyan ink has amaximum density in the 580 to 680 millimicron range and the black inkhas a high density throughout the visual band and also in the infra-redband. A given ink has its distinctive maximum density occurring at awavelength at which it has a relatively high density compared, eitherwith its own density in another range or with the density of another inkin the same range. This maximum density need not be an absolute maxias,cyan, yellow, and magenta are respectively the cor responding threecomplementary or subtractive primary non-spectrum colors. Accordingly,light reflecting from.

any one of these complementary colors will contain an increasinglysmaller component of its associated primary color as the density of thatcomplementary color increases. Stated differently, as the density of anon-spectrum complementary color increases, the absorption of itsassociated primary color also increases proportionately. This inventionhas applied this phenomena to a specific combination of elements toprovide valuable ink density data.

As above stated, blue is one of the primary colors and cyan is one ofthe complementary colors. Since both visually appear to be blue, cyanbeing blue-green, the printing trade frequently employs the name violetin lieu of the name blue. Hence, the terms blue. and violet" as employedherein, are to be considered synonymous in their reference to theadditiv primary color blue. In a preferred embodiment of the invention,a four channel scanner generates an output voltage proportional to thelogarithm of the ratio of the momentary photoelectric current to thephotoelectric current during passage of the highest reflection (usuallywhite) portions of the web. Accordingly, the voltage obtained from thefour channels of the scanner at the passage of these solid sample colorswould be:

If more or less ink is applied, then these signals will vary. It is seenthat change of density coverage of any one ink will influence more thanone of these responses. According to the invention, a resultant signalwhich is primarily a function of the coverage of one of the inks, isgenerated by mixing the scanner output signals in a suppression matrix.

For example, to eliminate the violet scanner response to magenta, andblack inks, a suitable fraction of the green and infra-red scanneroutput signals is substracted from the violet scanner output signal togenerate a signal responsive essentially to the coverage of the yellowink. Similarly, suitable fractions of all other scanner output signalsare subtracted from the green, red and infra-red output signals togenerate signals responsive essentially to the coverage of the magenta,cyan and black inks, respectively. A noted exception to the subtractiveoperation of the suppression matrix is with respect to the violetscanner response to cyan, in which a suitable fraction of the red outputsignal is added to the violet scanners output to complete the yellowdensity response signal. It will be noted that inclusion of infra-redinspection according to the present invention makes it possible todiscriminate black printing from a mixture of yellow, magenta and cyanprinting which can appear as black insofar as inspection with light inthe visible band is concerned.

FIG. 3 represents a portion of a web, say one page of the printedmaterial, having portions uniformly printed with a first color, sayyellow, on the area shown shaded with horizontal lines, and with asecond color, say magenta, on the area shaded with vertical lines andthe area upon which yellow was printed. It should be noted that the areacovered by both the yellow and magenta inks will appear as red. Theletters a, b, c, denote the centerlines of three tracks, chosen atrandom, along which this sheet may be inspected. These tracks may extendto a width of, say one-tenth of an inch right and left of thesecenterlines.

FIG. 4 represents the time curves of the violet and green phototubeoutput signals obtained by scanning these tracks. Va, Vb, Vc representthe violet output signals and Ga, Gb, Gc represent green output signals.These curves show the violet phototubes high sensitivity to the presenceof yellow ink and the green phototubes high sensitivity to the presenceof magenta ink. These curves also show the secondary sensitivity of theviolet phototube to the presence of magenta ink and that of the greenphototube to the presence of yellow ink. To eliminate these secondarysensitivities, the photoelectric output signals are transmitted (afteramplification) to a suppression matrix which will subtract from theviolet signal a part of the green signal and also subtract from thegreen signal a part of the violet signal. The output signals of thematrix are shown in FIG. 5. It is seen, that by proper selection of thefactors of the matrix, the violet photoelective output signal and thegreen photoelective output signal are transformed respectively intoyellow and magenta printing signals designated Ya, Yb, Y0 and Ma, Mb,Mc.

FIG. 6 represents a sheet, similar to FIG. 3, but here the yellow ink(represented by horizontal lines) is applied in three tones of dilferentdensity (represented by closer shading for heavier tone). Magenta ink isapplied at a constant tone over the area identified by vertical shading.

FIG. 7 represents the time curves of the photoelectric signals obtainedby scanning tracks a and b of this pattern. If these time curves areapplied to the same matrix used for obtaining the time curves of FIG. 6,output signals as shown in FIG. 8 will be obtained. In these curves ofFIG. 8, compensation is perfect only for the densities of the inks forwhich the matrix has been calibrated, while for other densities a slightsecondary effect of the unwanted color may persist.

This undesired side elfect can be dealt with in various ways. Nonlinearmatrices, which will subtract different fractions of the unwanted signalat difierent levels can be provided. Another economical way is tosubtract from each signal a derivative of another signal which isproportional to the derivative of the unwanted signal. A nonlinearmatrix may also be used for subtracting different fractions at diflerentvalues of wanted and of unwanted signal level. In practice, however, itwill usually suffice to adjust the herein preferably embodied linearmatrix for correct response at one maximum level of density.

Up to this point consideration has been given only to time curves ofphototube signals which, after passing the matrix, gave output signalsindicative of the densities of each of the inks used. Oscillograms orcurves of these signals will expand or contract as the area of the imageis changed. It would be diflicult to ascertain from observing thesecurves the amount of ink which is to be added or removed from theinspected track. To obtain clear and easily interpreted information ofthe desired type, scalar values, which increase or decrease according tochanges of the amounts or" the inks applied to the Web and theirappearance, are generated from these matrix output signals. Such scalarvalues can be generated from the output signals in various ways. Twovery useful scalars are those which are functions of the peak value orthe average value of the matrix output signal. However, other scalarvalues indicative of the application and appearance of the inks readilymay be obtained by means such as a detection circuit having a resistorin series with a diode. This provides a simple and efiicient means toalter the relative weight of peak value and average value componentswhich produce the scalar. FIGS. 9 and 10 represent two time curves withtheir average, peak, and a representative scalar value indicated by theheight of each identified horizontal line.

Thus far, the concepts of spectral curves, oscillogram's or time curves,and scalars have been explained as applied to the invention.Hereinafter, the mechanical structures and electrical circuits of thepreferred embodiment of the invention will be set out in detail.

FIG. 11 is a schematic cross sectional view of a scanner for theinspection of the web and the generation of photoelectric signalsindicative of the coverage of the printing thereon. A lamp 21 having afilament 22 is mounted on the scanner. A spherical or elliptical mirror23 concentrates the light of filament 22 onto an inspection zone 24,past which a web 25 moves in a direction perpendicular to the axialplane of the scanner. An achromatic objective lens 26 focuses an imageof the small portion of the web within the inspection zone through amask 27 and a lens 28 onto a dichroic mirror 29. The dichroic mirror 29reflects light of wavelength below 500 millimicrons and transmits lightabove 500 millimicrons. A simple lens 30 concentrates the lightreflected by mirror 29 on a circular portion of the cathode of aphototube 31 which is maximally sensitive to violet light. Between themirror 29 and phototube 31 is situated a filter 32 which removes certainundesired spectral components. In this manner, the phototube may be saidto generate a violet signal.

A dichroic mirror 33 which reflects light above 700' millimicrons andtransmits light below this, is located in the optical path of the lighttransmitted through mirror 29. A simple lens 34, and a filter 35, focusthe light reflected from mirror 33 onto a phototube 36, which generatesan infra-red signal. A simple lens 37 is used to collimate the beam oflight.

A dichroic mirror 38 reflecting light above 580 millimicrons andtransmitting light below that wavelength, lens 39, filter 40, andphototube 41 generate the red signal.

A dichroic filter 42, which reflects most of the remaining light, buttransmits some which forms an image on a ground glass plate 43, islocated in the optical path of the mirror 38. Lens 44, dichroic mirror45, used as a filter, and phototube 46, generate the green signal.

a The optical components of the scanner are enclosed within alight-tight enclosure 47. The ground glass plate 43 is covered by acover 48 which can be removed for inspecting the correct alignment ofmany of the optic elements lying between the inspection zone 24 and thisground glass plate, and replaced to prevent the intrusion of stray lightduring normal operation. The lamp 21 is placed outside the housing 47 toprevent stray light from affecting the phototubes and to avoid heatingof the phototubes. The four phototubes are shielded by individualshielding canisters one of which is shown at 51. Each phototube has anadjacent preamplifier electrometer tube 52 surrounded with a metallicshield 53 which. provides both electrical and optical shielding.

FIG. 12 represents the circuit diagram of a circuit constructedaccording to the invention. It is powered by a power supply, not shown,which may be common to a number of such amplifiers and which suppliesfilament voltage to the amplifier tubes and the direct voltagesrequired. The values of the latter are indicated in FIG. 12 adjacent theappropriate leads. The notation REG signifies a voltage regulated byvoltage regulating tubes or a combination of voltage regulating tubesand amplifier tubes or the like. In this figure, 61 represents aphototube, which is the equivalent of one of the phototubes 31, 36, 41or 46 of FIG. 11. Each of these phototubes is connected to an amplifiersimilar to the one shown in the presently discussed FIG. 12. A voltagedivider 62 supplies an anode voltage to the phototube. A diode 64connected to the voltage divider prevents the anode of electrometer tube63 from assuming a voltage above its rated value if unusual conditionsshould drive tube 63 into cut-off condition. An additional amplifyingstage, comprising triode 66, follows the electrometer tube amplifyingstage. A twin triode 70 provides two further stages of amplification andis followed by a phase splitter, comprising the duo-triode 75, having apair of cathode follower outputs 69a and 69b of opposite phase relation.

Thus, the output signal of phototube 61, substantially amplified,appears at output terminals 69a and 6%. At any given instant, themagnitudes of the signals appearing at 69a and 6% are equal, but theirpolarities are opposite; hence, if the signal at 69b is positive-going,the signal at 69a, is negative-going.

From the cathode follower output 6%, a resistor 76 leads to an area orpoint 77, to which one end of each of the resistors 79, 80, 81, 82 andof capacitor 83 is connected. The other terminals of resistors 80, 81,82 are connected to the outputs 69a of the amplifiers of the other threecolors of the same track, each resistor being connected to a differentamplifier. Inversely, the output 69a of tube 75 of each of the otheramplifiers is connected to the opposite terminal of the respectiveresistors of the three other amplifiers. These connections, symbolizedby arrowheads and resistors 76, 80, 81 and 82 and their counterparts inthe other amplifiers, are denominated as the suppression matrix.

The circuit of FIG. 12 functions in the following manner: Phototube 61is exposed to one of the spectrum components of the light reflected fromthe inspection zone and generates a voltage curve as shown in FIGS. 4 or7. Its anode is connected to a point carrying a positive voltage withrespect to ground and its cathode is connected to the grid ofelectrometer tube 63, whose filament is grounded. There exists no othergalvanic connection to the phototube cathode, so that whatever thephotocurrent may be, it flows through the grid-to-cathode path of tube63. This current generates a signal across this grid-tocathode pathwhich is proportional to the logarithm of the ratio of the instantaneousvalue of the photocurrent to the white level amount in accordance withprinciples explained in US. Patent No. 2,517,554. This signal appearsamplified at the anode of tube 63. Due to the low amplification factorinherent in the triode connection of the tube used, its anode can bedirect-coupled to the grid of the following tube 66, and an oscilloscopeconnected to this anode will display the oscillogram or time curve ofthe signal generated by the phototube 61, which is a func- 8 tion of thedensities of the inks as applied to the web at the inspection zone.

Through amplification in tubes 66, 170 and the signal generated byphototube 61 will appear amplified at the cathodes of tube 75. Thegreater the density of the nonspectrum ink on the portion of the webseen by phototube 61, the more positive will the signal be which appearsat the output terminal 69b. Its most negative voltage (pertaining to thepassage of white portions) is limited to a few volts above the 75 voltlevel by clamping diodes 73 and 74 connected between the 75 volt supplyand each of the grids of tube 75. An identical signal of oppositepolarity with similar white level appears at the output terminal 69a oftube 75.

Each of these signals in the four amplifiers represents one of theranges of wavelength of light reflected from I the web, i.e., violet,green, red or infra-red. Each signal 1 contains information relating thedensities of all the inks. To obtain information on the lack or excessof one ink; irrespective of lack or excess of the other inks, thesuppression matrix previously described is employed. In this embodimentof the invention, the matrix comprises four interconnected sets ofresistors 76, 80, 81, 82 in each amplifier. In each set, these resistorsare all connected to the junction point 77. i

In the violet amplifier, resistor 76 connects junction point 77 to theviolet density curve output terminal 6% on the second cathode of 75 ofits own circuit, whereas, resistors 80, 81, 82 connect it to the cathodeoutput terminals 69a of tubes 75 of the other (green, red, infrared)amplifiers inspecting the same inspection zone. By proper selection ofthese resistance values, the signal at point 77 can be made a functionprimarily of the excess or lack of yellow ink. Correspondingly, thesignals at points 77 of the green, red, infra-red amplifiers can be madefunctions primarily of the excess or lack of the magenta, cyan and blackink respectively.

For the mirrow-filter-phototube combinations described in connectionwith FIG. 11, satisfactory results have been obtained with the followingresistor combinations:

R76=:.33 megohm; violet amplifier 0.6 megohm to green,

3 megohms to red, 0.5 megohms to infra-red; green amplifier, 3 megohmsto violet, 2.2 megohms to red, .39 megohm to infra-red; red amplifier noresistor to violet, 7 megohms to green, .33 megohm to infrared; infraredamplifier: no resistor to violet or green, 2.2 megohms to red. All ofthese resistors are connected to the first cathode 69a of the respectivetube 75, except that the 3 megohm resistor from the violet amplifier isconnected to the sec-v 1 0nd cathode 69b of tube 75 of the redamplifier. This .fact is marked by the minus sign ahead of the value ofthis resistor. The reason for the necessity of adding rather thansubtracting this red correction to get true yellowinformation lies, itis believed, in the manner in which the presence of magenta ink aboveyellow ink may add to the reflection of certain spectrum components,especially insofar as small variations of heavy printing of this latterink are concerned.

In the present system it has been found necessary to eliminate thepossibility of some combination of correction signals from interferingwiththe white level of the main signal. This is accomplished by bringingthe white level of junction point 77 to 75 volts with the aid ofresistor 79 and clamping diode 78.

The density signals are transformed into representative scalars in thefollowing manner. In each amplifier, tube 84 amplifies the signalappearing at point 77;the resulting signal appearing at the right handcathode 84a of tube 84. Feedback resistor 97 insures that the amplifierstage will have the desired linear response. The signal at 84a is fed byway of capacitor 85 into the peak-to-peak detector series diodes 87. Inthis embodiment, in whichit is desired to obtain a representative scalarvalue less dependent on the peak values of density, as shown in FIGS.

9 and 10, a resistor 88 is connected in series with and a capacitor 86in parallel to the series diodes 87. A representative scalar signal,which is function of the lack or excess of one of the inks, now appearsat junction 87a of resistors 88 and 90 and capacitor 86. This junctionis connected through scalar detecting diode 89 to meter 94. This meterindicates the deviation of the representative scalar value from zerowhich is a function of the excess or lack of the monitored ink.

Meter 94 is a zero center instrument. Its midpoint indicates that therepresentative scalar signal equals the reference signal which isdetermined by adjusting potentiometer 96. Accordingly, the meter 94reads zero when a perfect copy is being scanned. Resistors 90, 91 and93, along with the +300 volt and 3O(l volt lines, comprise the meter 94bias supply. Meter readings are obtained by making the meter sensitiveto the difference in magnitudes of two currents flowing in oppositedirections in the meter. The first current is constant and flows fromground through the meter 94, resistor 93 and resistor 91 to the 300 voltline. The second current may be analyzed as having a magnitude dependenton the magnitude of the scalar signal and flowing from the +300 voltline through resistor 99, diode 89, resistor 93 and meter 94 to ground.Resistors 98 and capacitors 92 comprise a filter which together with thediode 89 form the scalar detecting circuit.

By means of this last detecting circuit the waveform appearing at thejunction 87a is detected into a DC. level suitable for causing the meter94 to indicate a stable scalar value. The actual current flowing throughthe meter will be controlled by diodes 87.

At a time when the press prints satisfactory copies, each of thepotentiometers 96 in each of the four scalar detecting circuits isadjusted until its meter 94 returns to its zero center. Thereupon, eachpotentiometer is locked in this position and thereafter the operatoradjusts the keys or other controls on the press until all meters returnto their zero center, again indicating perfect copy.

It is not necessary to have a number of scanners in fixed lateralposition, and, in a preferred embodiment of the invention, a scanner ismoved laterally across the width of the web for generating scalars foressentially the entire printed surface. FIG. 13 represents schematicallysuch an arrangement.

In this view, the housing of the scanner 47 is mounted on a guide shaft152 which is positioned across the entire width of the web 25. The webis supported by a guide roller 151. The guide shaft 152 slidably engagesa suitable passageway 154 in the scanner housing 47 and a threaded shaft153 engages a nut 155 which is fixed to the scanner housing 47.

A gear 160 is connected to the shaft 153 and to the printing cylinderssuch that the members move scanner housing 47 by the width of oneinspection track, for example, one tenth of an inch, for each revolutionof the printing cylinders. When scanner housing 47 reaches the end ofthe width of the web, a mechanism (not shown), reverses the direction ofthe drive and causes scanner housing 47 to move back in the oppositedirection.

In this manner, the scanner inspects one track of the web after theother and repeats this inspection (in the opposite direction) after ithas inspected all tracks. A 72" wide web inspected by 0.1 tracks wouldthus be reinspected after each 720 revolutions of the printingcylinders.

To further augment the monitoring of the densities of the non-spectruminks so that they can be maintained to proper standards, the presentinvention provides for a magnetic drum memory which first stores datarepresentative of proper ink density across the entire web and thencompares this data with the density of the ink being applied to themoving web.

As shown in FIG. 13, a cylinder or drum 156, having its surface coveredwith magnetizable material, is mounted on a shaft 157 which supports agear 159 that is coupled to the gear 160. In this manner, eachrevolution of the printing cylinders synchronously rotates the cylinder156 and the shaft 153. Secured to the scanner housing 47 is a bank offour magnetic recording and pickup heads 158, which is in closeproximity to the cylinders magnetizable surface s0 that as the rotatingshaft 153 causes the scanner housing to traverse the width of the web,the bank of magnetic heads similarly traverses the rotating cylinder156.

The bank of magnetic recording and pickup heads is so arranged that eachhead records or reads on a helix .025" wide. Thus, the magnetic headswill have a different location for any lateral position of the scannerand for any angular position of the printing cylinders. Hence, themagnetic information stored at any location of the cylinder 156 will beopposite the same head which stored this information each time thescanner is in the same lateral position inspecting the same inspectiontrack when the printing cylinders are in the same angular position.

The arrangement of FIG. 13 may be used with the same optical arrangementof the scanner head as shown in FIG. 11, and with an amplifier similarto the one shown in FIG. 12 connected with each phototube thereof. Torecord data concerning the desired density of non-spectrum inks to beapplied to a moving web and to compare the recorded data with thedynamically varying densities of these inks as they are being applied tothe web, this circuit can be altered by disconnecting capacitor and byconnecting the second cathode of twin triode 84 to the capacitor of anarrangement as shown in FIG. 14.

In this figure, series diodes 186 and 187 are connected to a junctionpoint 188-. A triode 19-1 is direct-coupled to the junction point 188-and anode modulates triode 192. The grid of triode 192 is connected to asource of ultrasonic oscillations 193, such as a piezo-electriccrystalresistor, and the resonant circuit 194 in its plate circuit istuned to the frequency of the oscillations from the generator 193. Thetuned circuit 194 comprises a transformer 195 the secondary of which canbe connected to or disconnected from a recording head 196 by one pole ofa double pole switch 197. The recording head 196 is also connected to astep-up transformer 198. The second pole of switch 197 connects theinput of tube 199 to the top of transformer 198 when transformer 195 isdisconnected from the recording head and connects the input of tube 199to a low tap of 198 when transformer 195 is connected to the recordinghead 196. The output of tube 199 is connected to series diodes 200. Theoutput of the series diodes 200 is connected to theresistance-capacitance. combination 201 and 202 and through resistor 293to grid of triode 204. Triode 21M- drives triode 205, the output ofwhich is applied through capacitor 206 to series diodes 187.

Contact sets 207 and 208 are two contact sets of a mechanical switchwhich is actuated by mechanical means, not shown. Contact set 207 canconnect ground to the junction of capacitor and resistor 189. Thisjunction is also coupled to the grid of tube 212 through capacitor 213.Contact set 208 can connect the plate of tube 212 to one or the othergrid of the two cathode followers provided by the twin triode 214. Thecathodes of tube 214 are connected to the vertical deflection plates ofa cathode ray tube 217.

The pattern appearing on the face of cathode ray tube 217 is shownschematically in FIG. 15. In this figure, the abscissas correspond tothe various lateral portions of the web. The heights of the trace aboveor below the zero line at the various abscissa are scalar values whichindicate excess or lack of ink each corresponding to one of the inksupply regulating keys. The horizontal zero line is not shownsuperimposed in FIG. 15 so as not to obscure the trace, but can be seenbetween many of the square waves of the trace. The vertical lines aremarkers injected after, say, every five keys for easy identification ofthe various keys on this pattern.

The arrangement described in connection with FIGS. 13, 14 and 15functions in the following manner when a new form (a new set of printingcylinders engraved for printing new information) is inserted into theprinting press. 7

First, all previous information is erased from cylinder 156. Next, thepressmen adjust all keys until they attain printing which issatisfactory in all respects. When this is achieved, they throw switch197 into the record position, connecting transformer 195 to therecording head 196. The switch is left in this position until thescanner has traveled once over the entire width of the web. After this,the switch 197 is thrown to its other position so that no newinformation is recorded on cylinder 156.

With switch 197 in this second position, the information recorded on thecylinder is transmitted via transformer 198 to tube 199. From then on,new information from the web as it is being printed, is correlated withthe information recorded on cylinder 156. This correlation yieldsvoltages at junction 188 positive or negative with respect to thejunction point of resistors 209 and 210 (as will be explained later)which charge capacitor 190. Each time the scanner reaches the end of thelateral region served by one key (and the start of the lateral regionserved by the next key), the twin switch 207, 208- discharges capacitor190 toward ground. The capacitor 190 starts anew in its assuming chargespositive or negative according to excess or lack of ink in theinspection track inspected. The discharge of 190 causes a voltage surgewhich is transmitted via capacitor 213 to tube 212. This signal isamplified and applied through contacts 208 to the left grid of 214 andto capacitor 215. This signal is then applied to one vertical plate ofcathode ray tube 217, which will be kept at a steady vertical deflectionpotential by reason of the charge in capacitor 215, until the next moveof contact set 208.

As will be noted, the charge on capacitor 190 will stay unchangedbetween two closings of switch 207 if and only if the average voltage ofpoint 188 over this period is zero. This average voltage will be zero ifthe signals impressed through capacitors 185 and 206 to diodes 186 and187, respectively, are equal. This equality for perfect copy is achievedby causing the signal appearing on the output of tube 205 to beidentical with the signal obtained from the perfect copies inspectedwhen switch 197' was set to recording.

It should be apparent from the above description that the invention iscapable of considerable variation and change well within the spirit andscope of the invention. Some of the applications of the invention havebeen discussed and others are deemed of suificient importance to mentionwithout further detailing the structure thereof.

The web 25 as described has not been categorized as opaqueintentionally. It may be translucent or transparent or it may beabsolutely opaque. In many instances, instead of reflecting light fromthe printed matter on the web, it may be more convenient or efficient toilluminate the inspection zone from the rear of the web and have thescanning device react to the transmitted light. This would requirelittle or no change in the specific structures illustrated, beyond thechange in the location of the illuminating means 21.

The invention herein is not limited to the indication of colorcondition, that is lack or excess of certain pigments. Since theindication is absolute, if it can be used to drive a meter, obviously itcan be used to energize structure which will add or subtract from thepigment, the latter effect being obtained, for example, by addingsolvent. Under such. circumstances, the judgment of the operator may bedispensed with.

The claims are to be interpreted to include such application.

What it is desired to claim is:

1. A density monitor for colored inks applied to a web, said monitorproviding bidirectional scalar indications of variation from normallydesired density of each of a plurality of inks as they are being appliedto the web, said monitor having means responsive to the amount of lightabsorption of each of said inks, comprising:

means for defining a discretely illuminated portion of said ink appliedweb and for receiving therefrom discrete spectrum components of thelight reflected from said web in proportion to the density of theapplied inks; said receiving means having means for separately responding to representative wavelengths of each of said spectrumcomponents and for transducing into electrical signals the quantum ofeach spectrum component in a manner which is primarily indicative of thedensity of its associated applied ink;

primarily substractive suppression matrix means cout pled to saidresponding means for receiving all of said electrical signals, operatingupon them in a primarily subtractive corrective mode, and removing fromeach said signal the influence of the inks associated with the other ofsaid signals;

said matrix means having a plurality of discrete outputs each of whichreceives from said matrix means energizations separately manifesting thedensity of each of said inks; and

a plurality of bidirectional scalar generating and indicating means eachrespectively coupled to one of said plurality of matrix outputs;

each said bidirectional scalar means having means for generating asignal characteristic of the desired density of its associated ink andcoacting this characterteristic signal with said matrix outputenergizations to provide dynamic bidirectional indications of thedensity of the then being applied ink as compared with.

its desired density.

2. A density monitor as defined in claim 1 in whichi said primarilysubstractive suppression matrix also has means providing additive modecorection to a cer tain portion of said electric signals.

3. A density monitor as defined in claim 1 in which:

said primarily substractive suppression matrix has a plurality of pairsof input terminals;

the terminals of each pair are of opposite polarity and are coupled toclamping means defining a voltage level representative of the web colorprior to the 7 application of any of said inks; and each pair ofterminals is associated with one of said inks. 4. A density monitor asdefined in claim 3 in which: each of said input terminals is part of aunidirectional conductive device which is intercoupled to the ter-.

minal of opposite polarity of each of the other pairs of input terminalsvia a plurality of discrete resistive 1 elements; and

each resistive element has a position and value for determining themagnitude and algebraic sign of said corrective mode.

5. A density monitor as defined in claim 4 in which:

the position of one of said resistive elements is such that it providesan algebraically additive correction to said otherwise subtractivematrix.

6. 'A density monitor as defined in claim 1 in which each saidbidirectional scalar generating and indicating 13 said meter, one ofsaid paths containing a constant current and the other path passingthrough said rectifier and having a magnitude dependent upon themagnitude of the density representing energizations from its matrixoutput.

7. A density monitor as defined in claim 1 in which:

one of said inks is black; and

said receiving and responding means comprises means maximally responsiveto wavelengths beyond the visible portion of the spectrum.

8. A density monitor as defined in claim 7 in which:

said receiving and responding means comprises dichroic elementsoptically coupled to a phototransducer selectively responsive towavelengths in the infra-red range.

9. A density monitor as defined in claim 1 further comprising:

means for recording and storing information corresponding to the desiredink density on a plurality of said discrete web portions;

means for subsequently reading this stored information andsimultaneously comparing it with the energizations from said matrixoutputs for the corresponding discrete web portions; and

means for indicating the results of said comparing.

10. A density monitor as defined in claim 1 and in which said web isadvanced longitudinally at a predetermined rate, further comprising:

a housing for said receiving and responding means; and

means mounting said housing adjacent said web and driving said housingtransverse to said web at a rate proportional to the advancing rate ofsaid web.

11. A density monitor as defined in claim 10 further comprising:

a magnetic drum memory mechanically linked to said mounting and drivingmeans for rotating said drum at a rate related to the transverse drivingof said housing; and

magnetic reading and recording means mechanically linked to said housingand electrically coupled to said matrix outputs.

12. A density monitor as defined in claim 11 further comprising:

electronic means coupled to said reading and recording means forenabling it to record on said drum memory data representative of thedesired density of inks to be applied across the web;

comparator means coupled to said reading and recording means and to saidmatrix outputs for synchronously comparing the density data recorded onsaid drum with the energizations from said matrix; and

optically persistent recording means coupled to said comparator meansfor providing at any one time information concerning the variations fromdesired density of the inks in a plurality of said discrete webportions.

13. A color monitor for providing an indication of the appearance ofeach of a plurality of different non-spectrum colored inks applied to aweb to form an image, the indications being representative of thedensities of the inks applied to the web, each ink having a maximumdensity in a range of wavelengths which is distinctively difierent fromthe ranges of Wavelengths at which the respective maximum densities ofthe other inks occur, which comprises:

means for illuminating a discretely small portion of the web having saidapplied image;

a plurality of photoelectric transducers disposed in the optical path ofthe light coming from the web, there being as many transducers asnon-spectrum inks it is desired to monitor;

each said transducer having means maximally reactive to the light comingfrom the web in one of the different ranges of wavelengths forgenerating an output signal which is a function of the densities of eachof the inks in the range of Wavelengths in which the transducer ismaximally reactive; one of said transducers being maximally reactive toand being optically coupled to elements reactive to the range ofinfra-red wavelengths for monitoring the density of non-spectrum blackink; matrix means connected to suppress that portion of each transduceroutput signal which is a function of the densities of all of the inksbut that ink having its distinctive maximum density in the range ofwavelengths at which the corresponding transducer is maximally reactive;said matrix means having a plurality of terminals and the outputsignals, after suppression, appearing at these terminals; and scalargenerating means connected to the matrix means terminals for providingquantitative scalar indications of the difference between the appearanceof each of the inks as applied to the web and the desired appearance inresponse to the resultant output signals. 14. The method of monitoringthe density of inks as they are being applied to a web, the increasingdensity of each said ink corresponding to an increasing absorption bythe ink applied web of the spectrum color complement 0 of the ink,comprising the steps of:

illuminating a discrete portion of the ink applied Web;

receiving from the web portion separate dynamic indications of thedensity of each ink in terms of the amount of absorption of its spectrumcolor complement;

generating separately signals which are functions of the separatelyreceived density indications,

suppressing in a primarily subtractive mode the portions of each of saidseparately generated signals which are attributable to all the inksexcept that which is attributable to a respective one of said inks, and

producing bidirectional scalar responses to each of the separatelygenerated and subtractively suppressed signals, each said response beinga scalar indication of the comparative dilference between the density ofeach of the applied inks and its desired density.

15. The method of monitoring as defined in claim 14 further comprisingthe steps of:

recording and storing information related to the desired density of theinks on a plurality of discrete portions of the web; subsequentlyreading the stored information and simultaneously comparing it with thescalar responses related to corresponding discrete Web portions;-and

indicating the results of said comparing in a visually perceptivemanner.

16. The method of monitoring the appearance of an image comprising aplurality of different colored inks applied to a Web, each ink having amaximum density in a range of wavelengths which is distinctivelydifferent from the range of wavelengths at which the respective maximumdensities of the other inks occur, one of said inks being black andhaving a distinctive range of wavelengths in the infra-red range, bymeans comprising a plurality of photoelectric transducers disposed inthe optical path of light coming from the web, there being as manytransducers as inks it is desired to monitor, each transducer havingmeans maximally reactive to the light from the web incident upon thetransducer in one of the distinctively different ranges of wavelengthsfor generating an output signal which is a function of the densities ofeach of the inks in the range of Wavelengths to which the transducer ismaximally reactive, a separate one of the transducers being respectivelyreactive to each of the distinctively difierent ranges of wavelengths oflight from the web the method comprising the steps of:

illuminating a portion of the web having the applied image;

generating output signals which are functions of the densities of theinks applied to the web, by scanning with the photoelectric transducersthe light coming from the web; suppressing that portion of eachtransducer output signal which is a function of the densities of all ofthe inks except that ink having its distinctive maximum density in therange of wavelengths to which the corresponding transducer is maximallyreactive; and generating scalars in response to the resulting transduceroutput signals, each of which is an indication of the difierence betweenthe appearance of one of the inks being monitored and the desiredappearance. 17. A color monitor for providing an indication of thedensity of each of a plurality of different non-spectrum colored inksapplied to a rapidly moving Web, each ink having a maximum density in arange of wavelengths which is distinctively different from the ranges ofwavelengths at which the respective maximum densities of the other inksoccur, which comprises:

means for illuminating a discretely small portion of the web, saidportion defining a narrow, generally longitudinal, uninterrupted zonewith respect to the moving web within the image bearing surface of saidrapidly moving web, said zone repeatedly incorporating contrastproducing areas for each of said inks, said areas having a significantlylighter density; and a plurality of photoelectric transducers disposedin the optical path of the light coming from said zone, each saidtransducer having means maximally responsive to the light coming fromsaid zone in one of the different ranges of wavelengths for generatingan output signal which is primarily a function of the differ- 16 encesbetween densities of each of the inks in said Zone and said contrastproducing areas therein for the range of wavelengths in which thetransducer is maximally responsive. 18. A color monitor as defined inclaim 17 in which: one of said transducers is maximally responsive tothe range of infra-red wavelengths for monitoring the density ofnon-spectrum black ink in contrast to a combination of colored inksproviding a black appearance.

19. A color monitor as defined in claim 17 further comprising:

matrix means connected to suppress that portion of each transduceroutput signal which is a function of the densities of all of the inksbut that ink having its distinctive maxi-mum density in the range ofwavelengths at which the corresponding transducer is maximallyresponsive.

20. A color monitor as defined in claim 19 in which:

said matrix means includes a plura'ity of terminals,

said output signals, after suppression, appearing at 1 these terminalsand further crnoprising:

scalar generating means connected to the matrix tmeans terminals forproviding in response to the resultant output signals quantitativescalar indications of the difference between the density of each of theinks as applied to the web and the desired density.

No references cited RALPH G. NILSON, Primary Examiner. J. D. WALL, M. A.LEAVITT, Assistant Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Pat t N 3,376,426April 2, 1968 Joseph C. Frommer et al.

It is certified that error appears in the above identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 1 line 33 "elemtromagnetic" should read Column 4 line 12 after"(infra-red)" electromagnetic insert a comma. Column 5 line 9 "magenta,"should read magenta Column 8 line 10, "substracted" should readsubtracted line 18 "web should read web; line 28 "circuit," should readcircuit; Column 12 line 5 16 37 and 41 "substractive", each occurrenceshould read subtractive Column 16, line 22 "cmoprising" should readcomprising Signed and sealed this 4th day of November 1969 (SEAL)Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

1. A DENSITY MONITOR FOR COLORED INKS APPLIED TO A WEB, SAID MONITORPROVIDING BIDIRECTIONAL SCALAR INDICATIONS OF VARIATION FROM NORMALLYDESIRED DENSITY OF EACH OF A PLURALITY OF INKS AS THEY ARE BEING APPLIEDTO THE WEB, SAID MONITOR HAVING MEANS RESPONSIVE TO THE AMOUNT OF LIGHTABSORPTION OF EACH OF SAID INKS, COMPRISING: MEANS FOR DEFINING ADISCRETELY ILLUMINATED PORTION OF SAID INK APPLIED WEB AND FOR RECEIVINGTHEREFROM DISCRETE SPECTRUM COMPONENTS OF THE LIGHT REFLECTED FROM SAIDWEB IN PROPORTION TO THE DENSITY OF THE APPLIED INKS; SAID RECEIVINGMEANS HAVING MEANS FOR SEPARATELY RESPONDING TO REPRESENTATIVEWAVELENGTHS OF EACH OF SAID SPECTRUM COMPONENTS AND FOR TRANSDUCING INTOELECTRICAL SIGNALS THE QUANTUM OF EACH SPECTRUM COMPONENT IN A MANNERWHICH IS PRIMARILY INDICATIVE OF THE DENSITY OF ITS ASSOCIATED APPLIEDINK; PRIMARILY SUBSTRACTIVE SUPPRESSION MATRIX MEANS COUPLED TO SAIDRESPONDING MEANS FOR RECEIVING ALL OF SAID ELECTRICAL SIGNALS, OPERATINGUPON THEM IN A PRIMARILY SUBTRACTIVE CORRECTIVE MODE, AND REMOVING FROMEACH SAID SIGNAL THE INFLUENCE OF THE INKS ASSOCIATED WITH THE OTHER OFSAID SIGNALS; SAID MATRIX MEANS HAVING A PLURALITY OF DISCRETE OUTPUTSEACH OF WHICH RECEIVES FROM SAID MATRIX MEANS ENERGIZATIONS SEPARATELYMANIFESTING THE DENSITY OF EACH OF SAID INKS; AND A PLURALITY OFBIDIRECTIONAL SCALER GENERATING AND INDICATING MEANS EACH RESPECTIVELYCOUPLED TO ONE OF SAID PLURALITY OF MATRIX OUTPUTS; EACH SAIDBIDIRECTIONAL SCALAR MEANS HAVING MEANS FOR GENERATING A SIGNALCHARACTERISTIC OF THE DESIRED DENSITY OF ITS ASSOCIATED INK AND COACTINGTHIS CHARACTERTERISTIC SIGNAL WITH SAID MATRIX OUTPUT ENERGIZATIONS TOPROVIDE DYNAMIC BIDIRECTIONAL INDICATIONS OF THE DENSITY OF THE THENBEING APPLIED INK AS COMPARED WITH ITS DESIRED DENSITY.